PROJECT SUMMARY/ ABSTRACT Many chronic, impairing, and costly adulthood health diseases, such as cardiovascular disease and type 2 diabetes, can be traced back to exposure to stress during childhood. One biological marker of physical health risk that may offer further insight into pathways by which chronic early stress leads to poor health outcomes is accelerated cellular aging, quantified as telomere length. Telomere shortening is already observable in young children who experience chronic exposure to stress, making telomere length an early biomarker of vulnerability to age-related diseases. Attachment theory offers an important framework for understanding the developmental origins of health and disease. Whereas sensitive parenting supports regulatory processes in early childhood, insensitive parenting may be a chronic stressor that undermines children?s physiological regulation, and subsequently the rate of children?s cellular aging. Adopting an intergenerational risk framework, the overarching aim of the proposed project is to examine whether mothers? attachment representations influence offspring?s telomere length through the quality of sensitive caregiving and children?s cortisol regulation. A total of 210 mothers and their young children will be drawn from two existing study samples: the first includes mothers and children from a diverse community sample, and the second includes mothers and children from a low-income community sample who previously participated in a randomized clinical trial of an attachment-based intervention. During infancy, we collected data on mothers? attachment representations, parental sensitivity, and children?s diurnal cortisol regulation. During follow-up visits conducted for the propose study when children are 4-5 years old, we will collect buccal cell samples to be assayed for telomere length. We will examine whether mothers? attachment representations affect children?s cellular aging (i.e., telomere length), whether parental sensitivity and children?s cortisol regulation mediate associations between mothers? attachment representations and children?s cellular aging, and whether the timing of sensitive parenting (manipulated via an attachment-based intervention) affects cellular aging.